The perception of odors requires olfactory information to be systematically organized in the brain. This organization, termed the olfactory map, consists of precise connections between olfactory receptor neurons and their postsynaptic targets. The molecular mechanisms responsible for olfactory map formation, however, is not well understood. I have discovered that Wnt2, a member of the conserved Wnt family of secreted proteins, is necessary for the organization of the Drosophila AL, an olfactory structure composed of olfactory receptor neurons (ORNs) that synapse upon projection neurons. In each All, axons expressing a given odorant receptor gene converge on a single glomerulus. The wnt2 gene plays a powerful role in specifying the precise connectivity of the Drosophila olfactory map by organizing the AL. Animals lacking a functional wnt2 gene exhibit severely disorganized, smaller ALs. Labeling of specific ORNs reveals that a large proportion of ORN axons are missing from the ALs and the structures of the glomeruli are severely degraded. Overexpression of Wnt2 induces the formation of ectopic synapses in the AL commissure, a structure normally composed of tracts of axons. I hypothesize that Wnt2 regulates both olfactory receptor neuron axon guidance and synaptic differentiation within the antenna lobe. The aim of this proposal is to investigate the role of Wnt2 in olfactory map formation by determining its cellular function, developmental requirements, and the cell types that express Wnt2. [unreadable] [unreadable] [unreadable]